An MPEG (Moving Picture Experts Group) 2 audio stream has backward compatibility so that it can be played back by even an MPEG1 audio decoder. In other words, the MPEG2 audio stream has a structure including an MPEG1 audio stream portion as a base portion and an MPEG2 audio portion as an extension portion thereof.
In the DVD (Digital Versatile Disc) video format, a technology for multiplexing an MPEG2 audio stream into a program stream is disclosed (e.g., Non-Patent Document 1). FIG. 1 is an illustration of the structure of a program stream 1 in the DVD video format. The program stream 1 in FIG. 1 includes a video pack 11, an MPEG2 audio pack 12, and a plurality of packs 13-1 to 13-j (j represents an arbitrary natural number).
The MPEG2 audio pack 12 includes a pack header 21, a PES (Packetized Elementary Stream) packet header 22, an MPEG1 audio data (Base) 23, a PES packet header 24, and an MPEG2 audio data (Extension) 25. In addition, the payload of the MPEG2 audio pack 12 includes an MPEG1 audio PES packet including the PES packet header 22 and the MPEG1 audio data 23, and an MPEG2 audio extension PES packet including the PES packet header 24 and the MPEG2 audio data 25.
When playing back the MPEG2 audio pack 12, a playback apparatus that can decode only an MPEG1 audio stream (playback apparatus only for MPEG1) separates and plays back only the PES packet header 22 and the MPEG1 audio data 23, which correspond to the MPEG1 audio stream portion. A playback apparatus that can perform decoding of up to an MPEG2 audio stream (playback apparatus capable of playing back up to an extension audio stream) separates and plays back both base and extension audio streams. Specifically, the latter playback apparatus plays back, in addition to the PES packet header 22 and the MPEG1 audio data 23, the PES packet header 24 and the MPEG2 audio data 25, which correspond to the MPEG2 extension audio stream.    [Non-Patent Document 1] DVD Specifications for Read-Only Disc Part 3; Version 1.1